We plan to determine the cellular mechanisms regulating the release of melanophore stimulating hormone (MSH) from the pars intermedia of the vertebrate pituitary. We hope to: (1) determine the nature of the neural factors such as catacholamines (norepinephrine, dopamine), acetylcholine, indoleamines (melatonin, serotonin) and hypothalamic peptides possibly involved in MSH release control; (2) determine the precise nature of the cellular receptors involved (dopaminergic, cholinergic, serotoninergic, etc.) and the mechanisms by which first messengers interacting with their respective receptors affect pars intermedia hormone secretion; (3) determine the role a second messenger such as cyclic AMP in the mechanism of MSH release; (4) determine the possible roles and mechanisms of actions and relationship to cyclic AMP of prostaglandins; (5) determine the ionic and metabolic requirements for MSH secretion; (6) determine the feasibility of tissue culture of pars intermedia cells as a means of delineating the basic biochemical events involved in pars intermedia physiology. Electron microscopy will be used as a tool to elucidate by histochemical methods certain biochemical and ultrastructural parameters possibly related to pars intermedia secretory mechanisms.